textproduct: Albany

WHAT HAS CHANGED

Though the Marginal Risk for severe weather remains in place across a large portion of eastern New York and western New England, the threat for severe thunderstorms this afternoon and this evening has diminished significantly. That said, the potential for non-severe thunderstorms remains elevated.

The storm total precipitation forecast has also increased, particularly for areas to the north and west of Albany where amounts from this morning's initial round of rainfall measured higher than previously expected.

KEY MESSAGES

1) Confidence is low in the development of severe thunderstorms this afternoon into this evening.

2) Additional periods of moderate to locally heavy rainfall this afternoon through early tomorrow morning will lead to minor to moderate river flooding in the western Mohawk Valley and isolated ponding of water in urban and poor drainage areas.

3) Numerous chances for rain over the coming seven days maintain the potential for additional minor river and urbanized flooding, though confidence is low in the overall flood threat at this time.

DISCUSSION

KEY MESSAGE 1...

Predominant southwesterly flow and eastward progressing outflow from upstream convection has allowed drier air to sneak into the region this afternoon, providing a respite from rainfall that has been ongoing for most of the day thus far. Finally, a few breaks in cloud coverage are appearing on visible satellite, allowing scattered, low-level billow clouds to be seen beneath thinning high clouds, particularly across the Southern Adirondacks and eastern Catskills. These clouds provide increased confidence in the validity of the capped to minimally surface- based unstable environment shown on the SPC Hourly Mesoscale Analysis page and hinted at in the latest HiRes soundings. As was the thought in the previous forecast, a stationary boundary remains in place just inside our northern CWA boundary with a parent area of low pressure spreading from southwest to northeast from northern Illinois to the eastern Great Lakes just to the west of the NY border. Stringing three low pressure centers together is a trailing cold front that extends as far south and west as the Southern Plains.

Flow aloft remains quasi-zonal with weak, embedded shortwaves in the mid-levels providing the primary upper-level forcing for ascent. Warm air and moisture advection in the broad pseudo-warm sector of the low pressure area has maintained mild temperatures and dewpoints across our forecast area, but this morning's rain and limited radiation have and should continue to maintain our low- level stable layer. This late in the day, it is going to be very difficult to erode this inversion, particularly due to the fact that persistent, though weak, warm air advection will prevent lapse rates from becoming steep enough to threaten any severe thunderstorm development. Therefore, most, if not all, instability that currently exists and persists across our area through this evening will remain elevated. That said, with sufficient elevated instability around 500-1000 J/kg and lapse rates maximizing around 6.5-7 C/km, the potential for non-severe thunderstorms still exits. For these reasons, we maintained the NBM slight chance to chance thunder within the showers that filter back into the region this afternoon through tonight ahead of and along the incoming cold front. It is also for these reasons that, in coordination with SPC and our neighboring offices, we have not issued a Severe Thunderstorm Watch at this time. An isolated severe thunderstorm with the primary threat of strong to locally damaging wind gusts certainly is a non-zero probability at this point, given some HiRes guidance solutions seem to either not resolve the aforementioned cap, or allow surface-based parcels to overcome it. But, confidence is high enough at this point to message that widespread severe convection is not likely this afternoon into this evening.

KEY MESSAGE 2... While forecast soundings aren't exactly alluding to severe convection this afternoon, they are certainly supporting efficient rainfall through tonight. Tall, skinny CAPE profiles and deep, moist thermal layers indicate the potential for moderate to locally heavy downpours particularly where any thunderstorms may develop. Additionally, the alignment of the southwesterly 925-850 mb nocturnal jet this evening just ahead of the front will enhance moisture transport into the region and possibly expand areas of moderate to locally heavy rainfall from the Southwest Adirondacks and western Mohawk Valley to areas farther south and east.

From the Capital District northward, about 0.25" to nearly 2" of rain has fallen thus far today. Given the favored environment for additional rainfall and potential heavier rates, another 0.5" to 1" is expected through tomorrow morning. The greatest rainfall is expected within the area currently under a Flood Watch (Southern Adirondacks and western Mohawk Valley), though the Eastern Catskills, Lake George-Saratoga Region, and Capital District could also see some higher QPF by tomorrow. There has already been minor to moderate flooding on the West Canada Creek with additional minor to potentially moderate flooding possible in the western Mohawk Valley through tomorrow morning. However, anywhere that gets some moderate to locally heavy rainfall rates could see some localized ponding of water in urban or poor drainage areas. Flash flooding, however, is not expected.

KEY MESSAGE 3... Thursday is looking to be a dreary day in store with overcast skies and medium to high (60-80%) chances for precipitation as our next weather system moves through eastern New York and western New England. The current forecast supports the precipitation type to be rain for most of eastern New York and western New England as temperatures stay above freezing. Locations for this exception are across the southwestern Adirondacks and high terrain of the southern Greens, where light freezing rain, then a light mix of rain and snow can occur Wednesday night into Thursday morning. Confidence continues to increase for periods. This could lead to a few slick spots on non-pavement surfaces in the southwestern Adirondacks and highest terrain locations of the southern Greens Thursday morning. Temperatures gradually rise Thursday morning to above freezing for precipitation to change over to plain rain. Precipitation chances decrease Thursday night to less than 50%. With the latest forecast supporting light precipitation amounts less a quarter inch, confidence continues to increase for no significant flooding impacts to occur for Thursday.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

A large cluster of showers and embedded thunderstorms is approaching the area from the west. While KPOU may stay just south of the bulk of the activity, the other sites will be impacted by rain, with thunder also expected for KALB and KPSF. IFR visibility of around 2SM within rainfall is expected for one to two hours at the start of the TAF period. Behind this batch of convection, some additional showers are possible through about midnight or so, but this activity will be more scattered and will include a TEMPO to address the variable conditions, with mainly MVFR within that activity. Winds will be south to southwest around 5-10 kts, although some locally higher gusts cannot be ruled out within thunderstorm activity. The bulk of the precip should be done for all sites towards 04z-06z or so.

While there will be limited precip for the late night hours, flying conditions may be VFR for a period with winds becoming west to southwest towards daybreak. As a frontal boundary drops southward out of the north, winds will become north to northwest on Wednesday morning. Flying conditions will lower to MVFR as low stratus develops behind the departing frontal boundary. These MVFR cigs will be in place all day, with a cooler northerly flow in place. Ceilings may be borderline IFR during the morning right behind the front at KGFL, but will keep MVFR for now. Some improvement is possible late in the day, but it will likely still be MVFR for all sites, although no precip is expected.

Outlook...

Wednesday Night: Moderate Operational Impact. Chance of RA. Thursday: Moderate Operational Impact. Chance of RA. Thursday Night: Moderate Operational Impact. Chance of RA. Friday: Moderate Operational Impact. Chance of RA. Friday Night: Moderate Operational Impact. Chance of RA. Saturday: Moderate Operational Impact. Chance of RA. Saturday Night: Moderate Operational Impact. Likely RA. Sunday: Moderate Operational Impact. Breezy. Likely RA.

ALY WATCHES/WARNINGS/ADVISORIES

CT...None. NY...Flood Watch through Wednesday evening for NYZ032-033-038. MA...None. VT...None.